1. Field of the Invention
The present invention relates to a spin-coating method for applying a coating liquid fed through a feed nozzle on a recording surface to form a coating layer, and a spin-coating apparatus including a control device.
2. Description of the Related Art
With increase in recording density of a magnetic recording medium, some proposals have been disclosed. In order to avoid a problem of superfluous recording called “side fringe”, a magnetic recording medium of a discrete track structure is disclosed in which a groove is provided between adjacent recording tracks. For the purpose of attaining enhanced recording density, Japanese Unexamined Patent Application Publication No. 2005-108351 discloses a patterned medium in which dots are formed on a disk, each dot being one bit of record.
Utilization of a nano-imprinting technique in the manufacturing process of such magnetic recording media has been proposed in Japanese Unexamined Patent Application Publication No. 2005-108351, for example. An imprinting apparatus for use in manufacturing a magnetic recording medium utilizing the nano-imprinting technique comprises, as shown in this patent application publication, main components of a press bottom board having a plate for mounting a substrate with a resist film, and a press top board allowing the approach to or departure from the press bottom board and having a disk-shaped stamper with a pattern of protrusions and recesses representing recording data in the central part thereof. In this structure of an imprinting apparatus, the stamper is pressed onto a resist film or a polymer layer formed on a recording surface of a magnetic recording medium, and the pattern of protrusions and recesses is transferred onto the recording surface of the magnetic recording medium.
Such a resist film is formed on a substrate by applying a photoresist uniformly on a magnetic film of the substrate by means of a spin-coating method as disclosed in Japanese Unexamined Patent Application Publication No. H10-249264, for example, and subsequently curing by ultraviolet light irradiation on the photoresist. It is required in the process that the resist film is formed with a uniform thickness over the whole substrate surface.
In order to form a protective film such as the resist film with a uniform thickness over the whole substrate surface, Japanese Unexamined Patent Application Publication No. H10-249264 discloses a technique in which a resin for the protective film is supplied from above the position of the center of rotation of the substrate down to the substrate. A rotary disk covering the center hole of the substrate is allowed to be held on or removed from a center hole of a turn table for mounting the substrate. A resin is fed onto the rotary disk while the rotary disk and the substrate are rotating, to form a protective film of the resin over the whole substrate surface.
The spin-coating method described above involves a problem that a photoresist fed around the periphery of the center hole of the substrate spreads irregularly and splashes on the edge of the center hole causing variation of film thickness in the radial direction. If the photoresist fed through a nozzle is arranged to avoid the splashing on the edge of the hole, that is, when an initial position of the tip of the nozzle is set at a position apart from the hole edge by a certain distance towards the outer peripheral side of the substrate in consideration of scattering and a wet range of the photoresist on the substrate, a film thickness in the center hole side of the substrate inner than the position of the nozzle tip may become extraordinarily thinner than other region of the substrate. Thus, uneven film thickness occurs in the resist film.
In the case a rotary disk covering the center hole of the substrate is provided as proposed in Japanese Unexamined Patent Application Publication No. H10-249264, photoresist is accumulated around the outer periphery of the rotary disk 2 in the resist film 6 formed extending over the outer periphery of the rotary disk 2 and the surface of the substrate 4 as shown in FIG. 7(A). As a result, as shown in FIG. 7(B), after the rotary disk 2 is removed from the center hole of the substrate 4, a thicker portion of the formed resist film 6′ than other portion is left at the position corresponding to the outer peripheral surface of the rotary disk 2. This configuration of the resist may cause difficulty in removing in a posterior step.
When the rotational speed of the turntable is raised, a thickness of the resist film on the substrate becomes thin and rather uneven in the region other than the part corresponding to the outer peripheral surface of the rotary disk 2. It has been confirmed that when the rotary disk 2 is composed of a material exhibiting poor wettability with the photoresist, the photoresist accumulates around the outer periphery of the rotary disk 2 and the formed resist film is bulged at the portion corresponding to the outer peripheral surface of the rotary disk 2 relatively to the other portion.